The Mercedes team has revealed that Russian Grand Prix winner Nico Rosberg set the fastest lap of the race on the "safe" settings of his power unit.

Although Rosberg dominated the race from start to finish, his day was not without problems, with the team revealing issues with his MGU-K late in the event.

In a demonstration of Mercedes' superiority, however, Rosberg set the quickest lap of the race with two laps to go, completing his first every 'grand chelem' (pole position, fastest lap and victory).

Although Rosberg's best lap was over six tenths of a second faster than anyone else - and set on used soft tyres - Mercedes revealed on Wednesday that it was actually set when the power unit was not performing at its peak.

Felipe Massa had the second fastest lap of the race, but on supersoft tyres. Ferrari's Kimi Raikkonen's best lap was a full second off Rosberg's.

"Shortly after his pitstop, we saw some alarming behaviour from Nico's MGU-K," said Mercedes in an open letter to the fans on Wednesday.

"We spent a number of laps reassuring him that he had a good gap over Lewis and could ease off before the FIA gave us the all-clear to tell him to switch to a setting that would control the issue.

"At the wheel, Nico wouldn't have had any inkling of the stress on the pit-wall. When he put in the fastest lap on the penultimate lap of the race, he was still in that 'safe' setting – demonstrating just how much pace the car had last weekend.

"This made Sunday all the more stressful for each of us. But, in the end, we were relieved just to get both cars to the flag."

With Hamilton also suffering problems, Mercedes insisted that it needs to continue to push to improve its reliability.

The team said the Briton had completed 16 laps with "zero" water pressure.

"Ultimately, none of this changes the fact that we have not met our own expectations in terms of reliability so far this season," it added. "Performance-wise we are right on the money – with a points haul just two shy of what we had managed by the same stage in 2015.

"But there is work to be done. Our goal is not simply to be fast but bulletproof too. Not just to manage problems but to understand them, fix them and ensure they are not repeated. We are working tirelessly to do just that and will continue to do so every step of the way.

"But there are no guarantees. This is a mechanical sport, balancing on the knife edge of performance and endurance. You have to push the boundaries and failures can happen."